"Waterless" cooking is old, as are knobs which give an audible signal when steam is formed to indicate attainment of cooking temperatures. Tops for cooking vessels which are provided with whistles and having means to turn the whistle off or to allow the escape of steam are also known. However, mechanically these are quite different from my device. Many such knobs cannot be disassembled. Those few which can be disassembled for cleaning could also release the knob portion accidentally under steam pressure, which might well cause loss of the knob or even injury.
Slide valves are of course known in other connections but a slide valve possesses unique advantages in a whistle knob. Likewise, the method of assembly is believed to possess unique advantages.